Treatment of organic derivatives of cellulose



Patented Jan; 18, 1938 UNITED STATES TREATMENT OF ORGANIC DERIVATIVES OFCELLULOSE William Whitehead, Cumberland, Md., assignor to CelaneseCorporation of America, a corporation of Delaware No Drawing.Application September 30, 1936, Serial No. 103,397

10 Claims.

This invention relates to the treatment of organic derivatives ofcellulose, such as the organic esters of cellulose, to remove therefrom,or to make inactive, corrosive compounds or com- 5 pounds that cause theorganic derivatives of cellulose to have a corrosive efiect on metallicsurfaces. The so treated organic derivatives of cellulose may be formedinto filaments, films and molded articles without appreciably corrodingthe spinning jets or other metallic surfaces contacted by solutions ofthe organic derivatives of cellulose.

An object of the invention is the economic and expeditious production oforganic derivatives of cellulose that, when dissolved in a. solvent,form solutions that are less corrosive than similar solu tions formed ofuntreated organic derivatives of cellulose. Other objects of theinvention will appear from the following detailed description.

In the production of organic derivatives of cellulose there are producedvarious compounds that are either corrosive to metals or, when anorganic derivative of cellulose is dissolved in a solvent therefor,cause the formation of compounds that are corrosive to metals. Examplesof one type of such compounds are those containing sulphur either aslabile sulphur bodies or the less labile sulphur bodies of a higherdegree of oxidation. These corrosive bodies also form with the metalsinsoluble compounds or compounds which are less readily dispersed andare less stable when dispersed, and further these bodies undergochanges, both physical and chemical, resulting in agglomeration, chokageof filters, lining jet orifices, etc. These compounds, prior to thisinvention, were separated from the derivatives of cellulose, if at all,only by elaborate and involved treatments. By employing this invention,however, organic esters of cellulose either before, during, or afterbeing stabilized, are treated with an agent that tends to removecorrosive compounds, or compounds Which tend to produce corrosivecompounds. The treatment in accordance with this invention is carriedout to such an extent as to produce an organic derivative of cellulosethat is substantially noncorrosive and is completed in a short period oftime. The treatment in accordance with this invention also increases thestability of cellulose esters to ageing and heat.

Organic derivatives of cellulose treated in accordance with thisinvention may be spun into filaments by extruding the same through jetsinto a solidifying medium. The organic derivative of cellulose sotreated does not attack the metal surrounding the orifice. When themetal of the spinning jet is attacked, the size of the orifice isenlarged or particles of the corroded metal are wedged in the orifice,thus producing filaments of undesired denier. Furthermore, since organicderivatives of cellulose treated in accordance with this invention donot attack metal parts contacted thereby, they do not pick up metallicsalts which tend to discolor articles formed therefrom.

In accordance with this invention I treat precipitated or solid organicderivatives of cellulose, preferably at elevated temperatures, with adilute solution of oxalic acid. After this treatment, the derivatives ofcellulose may be washed substantially free of the oxalic acid and/or thereaction products formed by same. If desired the organic derivatives ofcellulose, after treatment with oxalic acid, may be drained and driedleaving at least a trace of the oxalic acid in the organic derivativesof cellulose. The organic derivatives of cellulose may be treated beforeor after a treatment with the oxalic acid with chlorine or achlorine-liberating compound such as sodium hypochlorite. An organicderivative of cellulose thus treated, when dissolved in a solventtherefor, forms a solution which is substantially noncorrosive.

This invention is especially applicable to the treatment of any organicesters of cellulose such as cellulose acetate, cellulose formate,cellulose propionate and cellulose butyrate that are formed by processeswhich tend to produce corrosive materials. It is also applicable in anobvious way to the treatment of corrosive nitrocellulose, celluloseethers and mixed esters and ethers of cellulose. Examples of celluloseethers are ethyl cellulose, methyl cellulose and benzyl cellulose.

The organic esters of cellulose that lend themselves to this inventionmay be made by any of the methods now employed to make the same. Forexample, cellulose (cotton linters, cotton, wood pulp, etc.) with orwithout a pretreatment in organic acid such as acetic acid and formicacid, is esterified by treating the same with an acid anhydride in thepresence of an acid solvent and a catalyst. In place of the acid solventor in connection therewith, there may be used suspension liquids such asbenzol. The acid solvent may be a concentrated acid corresponchng to theanhydride employed or it may be, as is preferred, glacial acetic acid.Examples of catalysts are sulphuric acid, phosphorous acid,hydrochlorite acid, zinc chloride and mixtures of these.

After esterification, sufficient water may be added to convert anyremaining anhydride to the corresponding acid and the mixture hydrolizedor ripened until the desired solubility charactersteam with or withoutpressure. Although stabilized, the ester may containcompounds which,

when the ester is in solution, cause the solution to corrode or attackmetals.

I have found that, if the ester is treated after precipitation, butprior to stabilizing, by soaking, the ester in a dilute aqueous solutionof oxalic acid, the resulting ester is substantially free of compounds,the exact chemical structure of which is unknown, that cause the esteror solutions thereof to have a corrosive effect on metals. I have alsofound that theseundesirable compounds may be removed or diminished tobelow an effective quantity by soaking the stabilized, J ester in adilute solution of oxalic acid. The

latter method of treating-stabilized esters is preferable as it is ingeneral more effective and has less tendency to alter the viscosity andsolubility characteristics of the. ester. The soaking treatment ispreferably carried on at elevatedtemperature, for instance, at from 50to 100 C. Although soaking a precipitated derivative of cellulose in adilute solution of oxalic acid is a preferred method, other methods maybe employed such as spraying said solution on the derivative ofcellulose or workingi-he derivative of cellulose in a countercurrentmanner in a stream of said solution.

The treating liquid or bath may be formed by dissolving a suitablequantity of oxalic acid in water. When treating organic esters ofcellulose, the percentage of oxalic acid in the treating bath should beso regulated that there is present in the bath from between 0.03 to 1%of oxalic acid on the weight of the organic esterof cellulose beingtreated. The amount of the aqueous solution of oxalic acid is preferablyfrom 4 to 20 or more times the weight of the derivative of cellulose.Although the treating bath may be of any suitable temperature, forinstance, from 50 to 100 0., it has been found. preferable to maintainthe temperature at from 80 C. to the boiling point of the bath. Thelength of time required to treat a batch of the organic esters ofcellulose will depend somewhat upon the original corrosive properties ofsame and upon the temperature and concentration of the oxalic acidsolution- In general, soaking the organic ester of cellulose from l'to 5hours at or near the boiling point of the bath has been foundsufiicient.

' The treatment of the derivative of cellulose with the aqueous solutionof oxalic acid may be preceded or followed by a treatment with analkaline hypochlorite. The alkaline hypochlorite treatment is not.absolutely necessary. The treatment with the oxalic acid solution issufficient to form non-corrosive derivatives of cellulose where it isundesirable to use thereon chlorine bleaching agents.

To further describe the invention and not as a limitation, the followinexamples are given:

Example I Precipitated unstabilized cellulose acetate, after beingwashed to neutral state, is boiled for 4 hours in. an aqueous bathcontaining 0.03% on the Weight of the cellulose acetate of oxalic acid.The bath is approximately 20 times the weight of thecellulose acetate.The treating bath is .drained from the cellulose acetate and thecellulose acetate stabilized in a normal manner,washed,.dried anddissolvedin a suitable solvent. The resulting solution is found to besubstantially free of any corrosive compounds.

Example II Precipitated stabilized cellulose acetate, after being washedto neutral state, is boiled for four hours in an aqueous bath containing0.04% on the weight of the cellulose acetate of oxalic acid. The bath isapproximately 20 times the weight of the cellulose acetate. Thecellulose acetate is washed, dried and dissolved in a suitable solvent.Theresulting solution is found to be substantially free of any corrosivecompounds with a much reduced S04 content.

It is to be understood that the foregoing detailed description is givenmerely by way" of illustration and that many variations may be madetherein without departing from the spirit of my invention.

Having describedmy invention, what I desire to secure by Letters Patentis:

1. Method of reducing the corrosive properties of a derivative ofcellulose, which comprises treating a stabilized derivative of cellulosewith oxalic acid for a period of at least one hour.

2. Method of reducing the corrosive properties of an organic ester ofcellulose, which comprises treating a stabilized organic ester ofcellulose with oxalic acid for a period of at least one hour.

3. Method of reducing the corrosive properties of cellulose acetate,which comprises treating a stabilizedcellulose acetate with oxalic acidfor a period of at least one hour.

4. Method of reducing, the corrosive properties of an organic ester ofcellulose, which comprises treating a stabilized organic ester ofcellulose with a dilute solution of oxalic ,acid for a-period of atleast one hour.

5. Method of reducing the corrosive properties of cellulose acetate,which comprises treating a stabilized cellulose acetate with a dilutesolution of oxalic acid for a period of at leastone hour.

6. Method of reducing the corrosive properties ofcellulose acetate,which comprises treating a stabilized cellulose acetate with a diluteaqueous solution of oxalic acid for a period of at least one hour.

'7. Method-of reducing the corrosive properties of an organic ester ofcellulose, which comprises treating at elevated temperatures astabilized organic ester of cellulose with oxalic acid for a period ofat least one hour.

8. Method of reducing the corrosive properties of an organic ester ofcellulose, which comprises treating a stabilized organic ester ofcellulose with a boiling solution of oxalic acid for a period of atleast one hour.

9. Method of reducing the corrosive properties of cellulose acetate,which comprises treating a stabilized cellulose acetate with an aqueoussolution containing from 0.03 to 1.0%,] based on the weight of thecellulose acetate'present, of oxalic acid for a period of at least onehour.

10. Method of reducing the corrosive properties of cellulose acetate,which comprises treating at elevated temperatures a stabilized celluloseacetate with an aqueous solution containing from 0.03 to 1.0%, based onthe weight of the cellulose acetate present, of oxalic acid for a periodof at least one hour.

WILLIAM WHITEHEAD.

